1. Field of the Invention
The present invention relates to a multi-band flat antenna, and more particularly to a flat antenna having a meandering configuration constructed in such a way that conductive traces are printed on multiple layers of dielectric substrates and electrically connected by a plated through hole (PTH) process. The flat antenna is suitable for use in any wireless equipment such as a wireless mobile phone, a wireless modem or for use in a local area network (LAN).
2. Description of Related Art
The rapid developments in the wireless communication field have led to a variety of new communication apparatuses and technologies in recent years. Basically, these communication products are required to be multi-functioning in a miniature size. Such requirements are also applied to wireless antenna used with the new communication products. For the third generation wireless format (3G), it is particularly necessary to develop a novel antenna that can satisfy requirements of being multi-functioning, multi-band and compact. Actually, many manufacturers in this field have continuously proposed different antenna.
With reference to FIG. 1, an antenna (60) capable of providing dual operation bands includes a long conductive wire (61) and a short conductive wire (62) apart from the long conductive wire (61) by a distance. Two distal end of the wires (61)(62) are in the open circuit status, but the other ends of which are commonly connected by a feeding port (63). The long conductive wire (61) is operated at a low frequency, for example 900 MHz, while the short conductive wire (62) is operated at a high frequency, for example 1800 MHz. Although the antenna (60) can be operated at two different bands, the antenna is still practical to be integrated in the small communication products because the length of the wire (61) is too great.
With reference to FIG. 2, to solve the length problem of the above-mentioned antenna, a flat antenna structure consisting of a substrate (70) on which a meandering radiator (71) is proposed. Another alternative type is shown in FIG. 4, wherein a conventional chip antenna is formed by a spiral conductive wire (81) embedded in a solid substrate (80). Using the antennae of FIGS. 2 and 4, the foregoing wire (61) for the low operation band in the dual antenna (60) is able to be replaced by either type. For example, a first meandering radiator (71) and a second radiator (72) are created on a flat substrate (70) as shown in FIG. 3, or a spiral conductive wire (81) and a second wire (82) are formed inside a substrate (61) to provide different operation bands. However, the size of these antennae still can not be effectively miniaturized to meet the desired requirement.
Besides the aforementioned miniature size requirement, a wireless antenna needs to encompass multiple channels and be able to support wide operation frequency bandwidth. For example, some established operation frequency standards may include EGSM (880–960 MHz), DCS (1710–1880 MHz), PCS (1850–1990 MHz), WCDMA/CDMA2000 (1920–2170 MHz), IEEE802.11b (2.4–2.4835 GHz). These standards can be mainly categorized into some groups based on an operation frequency band, i.e. a first operation frequency band (880–960 MHz) with 80 MHz bandwidth, a second operation frequency band (1710–2170 MHz) with 460 MHz bandwidth, and a third operation frequency band (2.4–2.4835 GHz) with 83.5 MHz bandwidth.
As discussed above, the miniature size and multi-channel are essential factors for the antenna. However, since multiple radiators of different frequency bands are all formed on the same substrate, interference problems existing among the radiators is another critical issue for consideration. As a result, the practical development of the antenna must simultaneously take into account many aspects including the size and performance.
The antenna of the wireless communication products can be distinguished into the external type and the internal type based on their installation position. The most commonly used external type antenna has a circular appearance if the antenna is created as a spiral configuration. To vary the appearance of the antenna, the flat structure is suitable for forming a rectangular, square or an elliptical antenna.
Moreover, the chip type antenna also can be implemented by the flat structure. The antenna can be electrically mounted on a desired circuit board by the surface mounting technology (SMT) thus reducing the cost of packaging and connecting processes. Consequently, the flat structure is quite suitable for use as an internal type antenna.